Combustion engines commonly employ exhaust gas oxygen sensors, such as universal exhaust gas oxygen (UEGO) and heated exhaust gas oxygen (HEGO) sensors, to measure the air-fuel ratio (AFR) of the engine exhaust. The AFR measured by the exhaust gas oxygen sensors is fed back to a closed-loop engine fueling controller that responsively adjusts bank-wise fueling to the engine to achieve a target overall AFR (e.g., stoichiometric engine operation, □=1) for each bank of cylinders. Operating near stoichiometric AFR enables the engine to operate more efficiently, with reduced emissions. The feedback control algorithms can employ adaptive learning to reduce closed-loop fueling errors and to reduce overall bank to bank fueling variability.
However, bank-wise fueling control algorithms do not address individual cylinder to cylinder AFR variability during engine operation. In particular, bank-wise fueling may achieve a target overall AFR averaged over all cylinders in a bank; however, individual cylinder AFR values can fluctuate above and below the target AFR value. Imbalances in individual cylinder AFR may cause fuel injector imbalances, intake air charge and distribution errors, combustion variability, and fueling variability. Consequently, individual cylinder AFR variability can lead to reduced engine performance (e.g., higher torque variability, reduced vehicle drivability, increased NVH, and the like) and increased emissions.
The inventors herein have recognized the above issues and have devised numerous approaches to at least partially address them. In one example, a method for an engine may comprise, measuring a high-frequency exhaust gas composition, and for a first cylinder of the engine, parsing the measured high-frequency exhaust gas composition to determine a first cylinder-specific component of the high-frequency exhaust gas composition, estimating an air-fuel ratio (AFR) based on the first cylinder-specific component of the measured high-frequency exhaust gas composition, and correcting the estimated AFR by subtracting intercylinder exhaust gas interactions from the estimated AFR. In this way, AFR variability between individual cylinders of a combustion engine can be reduced, thereby increasing vehicle drivability, reducing engine NVH, and reducing emissions. As one example, individual cylinder AFR values in a bank can be determined from a single high-frequency exhaust gas composition sensor positioned in the exhaust manifold. Thus, individual cylinder AFR variability may be reduced, while maintaining and/or reducing engine manufacturing cost and complexity.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.